A new version of the SGE has been released. This features two changes to the SGE specification:

sge.dsp.Object now supports an "image_blend_mode" attribute, which allows you to specify blend modes other than multiply to use for colorizing the image.

Sprites treated as transparently no longer implicitly use the top-right pixel as a colorkey when no transparency is found in the image. This change was made for two reasons: one, this system was really finnicky and user-unfriendly (it meant that simple image format conversions could screw up how images look in-game), and two, it caused a bug in the Pygame SGE that I couldn't fix. I think making all colorkey use explicit is ultimately the best thing to do.

Additionally, the Pygame SGE has the following changes:

The method of adjusting alpha transparency with the image_alpha attribute of objects has been tweaked. The difference is not terribly noticeable, but it's an improvement.